Image processor

ABSTRACT

An image processor containing an EPROM ( 38 ) stored with coefficient data for image enlargement and reduction, coefficient read controllers ( 40-44 ) for reading out coefficient data from the EPROM ( 38 ) according to an enlargement/reduction selection signal, a variable horizontal characteristic filter ( 16 ) for executing either image enlargement or image reduction according to the coefficient data, a variable vertical characteristic filter ( 18 ) also for executing either image enlargement or image reduction according to the coefficient data, a frame memory ( 20 ), a contour correcting circuit ( 14 ), and selectors ( 22-30 ). When image enlargement is selected by selectors ( 22-30 ), input video signals are processed by the contour correcting circuit ( 14 ), the frame memory ( 20 ), and the filters ( 16,18 ) in this order while, when image reduction is selected, input video signals are processed by the same in the reverse order. The portion which should not undergo contour enhancement does not undergo contour enhancement during image enlargement, and high frequency components enhanced by contour correction during image reduction do not disappear and adequate contour correction, even when either processing image enlargement or reduction, is selected.

TECHNICAL FIELD

The present invention relates to an image processor designed for eitherimage enlargement processing or image reduction processing or the bothor contour correction.

BACKGROUND ART

It is a common practice for conventional image processors to execute theimage processing in the order of the contour correction to input videosignal and subsequent image enlargement processing and/or imagereduction processing, or in the order of the image enlargementprocessing and/or image reduction processing and subsequent contourcorrection.

In other words, the contour correction is not correlated with the imageenlargement processing and/or image reduction processing.

Further, as discussed above, in a conventional image processor, thecontour correction is not correlated with the image enlargementprocessing and/or image reduction processing, causing a problem such asvery poor contour correction effect or unnecessary contour emphasis.

For instance, in a system designed for making the contour correctionsubsequently to the image enlargement processing to the input videosignal, the contour correction is made to the video signal subsequentlyto the image enlargement processing, causing a problem such as makingunnecessary emphasizing of contour.

Further, in a system designed for executing the image reductionprocessing subsequently to the image reduction processing for inputvideo signal, the band of the high-pass frequency component intensifiedby the contour emphasizing is limited in the stage of image reductionprocessing, thereby causing a problem that very poor contour correctioneffect results.

The present invention is made in consideration of the above problems andis designed to provide an image processor that is not only capable offreely selecting either the image enlargement processing or imagereduction processing but also capable of making appropriate contourcorrection regardless of whether the image enlargement processing orimage reduction processing is selected.

DISCLOSURE OF THE INVENTION

The image processor according to the present invention comprises acoefficient memory for previously storing the coefficients for imageenlargement and image reduction, a coefficient read-out controller forreading out corresponding coefficient from the coefficient memoryaccording to enlargement/reduction selection signal, a characteristicvariable filter for executing the filter processing corresponding toeither image enlargement or image reduction according to the coefficientdata read out by the coefficient read-out controller, an image memoryand a contour correction circuit and selector groups, the selectorgroups being respectively provided in the preceding and subsequentstages of each of the image memory, the contour correction circuit andthe characteristic variable filter and connected to one another.

When the image enlargement processing is selected by theenlargement/reduction selection signal, the selector groups makes theinput video signal being processed sequentially through the contourselection circuit, image memory and characteristic variable filter,while the video signal is made to be processed sequentially through thecharacteristic variable filter, image memory and contour correctioncircuit when the enlargement/reduction selection signal for imagereduction processing is selected.

When the image enlargement processing is selected, the input videosignal is made to be processed sequentially through the contourcorrection circuit, image memory and characteristic variable filter. Inthis case, the characteristic variable filter executes the filterprocessing for image enlargement according to the coefficient data readout from the coefficient memory in response to the enlargement/reductionselection signal. In this case, since the image enlargement processingis executed after the contour correction, unnecessary emphasizing ofcontour can be prevented unlike the case of the conventional systemwherein the contour correction processing is applied to the video signalwhich has already undergone the image enlargement processing.

When the image reduction processing is selected, the input video signalis processed sequentially through the characteristic variable filter,image memory and the contour correction circuit. In this case, thecharacteristic variable filter executes the filter processing for imagereduction according to the coefficient data for the image reduction readout from the coefficient memory in response to the enlargement/reductionselection signal. In this case, since the contour correction is madeafter the image reduction processing, the band of the high-passfrequency component will not be limited for the image reductionprocessing unlike the case of the conventional system.

Further, in the image processor according to the present invention, thecoefficient memory previously stores the coefficient data for imageenlargement and image reduction in horizontal direction and verticaldirection respectively; the coefficient read-out controller reads outthe corresponding coefficient data from the coefficient memory accordingto the enlargement/reduction selection signal for selecting either imageenlargement processing or image reduction processing with respect toeach of the horizontal direction and vertical direction; thecharacteristic variable filter comprises a horizontal characteristicvariable filter, for executing the filter processing for either theimage enlargement processing or image reduction processing in horizontaldirection according to the coefficient data for horizontal directionread out by the coefficient read-out controller, and a verticalcharacteristic variable filter for executing the filter processing foreither the image enlargement processing or image reduction processing invertical direction according to the coefficient data for verticaldirection read out by the coefficient read-out controller.

With the arrangement described above, either the image enlargementprocessing or image reduction processing, each with respect to eitherhorizontal direction (transverse direction) or vertical direction(perpendicular direction) can be selected freely.

In the image processor according to the present invention, when thevertical reduction and horizontal reduction are selected by the selectorgroups, processing proceeds sequentially through the horizontalcharacteristic variable filter, vertical characteristic variable filter,image memory and contour correction circuit; when the vertical reductionand horizontal enlargement are selected, the processing proceedssequentially through the vertical characteristic variable filter, imagememory, horizontal characteristic variable filter and contour correctioncircuit; when vertical enlargement and horizontal reduction areselected, the processing proceeds sequentially through the horizontalcharacteristic variable filter, image memory, vertical characteristicvariable filter and contour correction circuit; when the verticalenlargement and horizontal enlargement are selected, the processingproceeds sequentially through the contour correction circuit, imagememory, horizontal characteristic variable filter and verticalcharacteristic variable filter.

With the arrangement described above, when the image enlargementprocessing or image reduction processing is selected, each with respectto both the horizontal and vertical directions, not only the appropriatecontour correction can be accomplished but also it can be prevented thatthe contour correction effect becomes ineffective when the imageenlargement processing in vertical direction is selected while the imagereduction processing in horizontal direction is selected and vice versa.

Further, in the image processor according to the present invention, whenthe vertical reduction and horizontal reduction are selected by theselector groups, the processing proceeds sequentially through thehorizontal characteristic variable filter, vertical characteristicvariable filter, image memory and contour correction circuit; whenvertical reduction and horizontal enlargement are selected, theprocessing proceeds sequentially through the contour correction circuit,vertical characteristic variable filter, image memory and horizontalcharacteristic variable filter; when vertical enlargement and horizontalreduction are selected, the processing proceeds sequentially through thecontour correction circuit, horizontal characteristic variable filter,image memory and vertical characteristic variable filter; when verticalenlargement and horizontal enlargement are selected, the processingproceeds sequentially through the contour correction circuit, imagememory, horizontal characteristic variable filter and verticalcharacteristic variable filter.

With the arrangement described above, when the image enlargementprocessing or image reduction processing is selected with respect toboth the horizontal and vertical directions, not only appropriatecontour correction can be accomplished but also unnecessary emphasizingcan be prevented when image enlargement in horizontal direction isselected while image reduction in vertical direction is selected andvise versa.

Further, in the image processor according to the present invention, thecontour correction circuit comprises a horizontal contour sampler forsampling the contour component in horizontal direction, a verticalcontour sampler for sampling the contour component in verticaldirection, a first adder for adding the contour component sampled by thehorizontal contour sampler and the contour component sampled by thevertical contour sampler and a second adder for adding the contourcomponent outputted from the first adder to the video signal to beinputted to the contour correction circuit to output the video signalcorrected for contour.

With the arrangement described above, the contour can be corrected bysampling and adding the contour components in horizontal direction andvertical direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an embodiment of the image processoraccording to the present invention.

FIG. 2 is a block diagram showing an example of the contour correctioncircuit 14 given in FIG. 1.

FIG. 3 is a block diagram showing an example of the horizontalcharacteristic variable filter 16 given in FIG. 1.

FIG. 4 is an explanatory drawing for showing the operations of theselector groups 22 through 32 and decoder 36 given in FIG. 1.

FIG. 5 is an explanatory drawing for indicating the sequence ofprocessings to be executed when “vertical reduction and horizontalreduction processing”, “vertical reduction and horizontal enlargementprocessing”, “vertical enlargement and horizontal reduction processing”and “vertical enlargement and horizontal enlargement processing” areselected respectively.

FIG. 6 is an explanatory drawing for comparing the frequencycharacteristic (of the image processor according to the presentinvention), in the case where the image reduction processing (e.g.,“vertical reduction and horizontal reduction”) is selected, with that ofa conventional image processor (an example for comparison), wherein (A)represents the case of the present invention, while (B) represents thecase of the conventional image processor (an example for comparison).

FIG. 7 is an explanatory drawing for comparing the frequencycharacteristic of (the image processor according to the presentinvention), in the case where the image enlargement processing (e.g.,vertical enlargement and horizontal enlargement) is selected, with thatof the conventional image processor (an example for comparison), wherein(A) represents the case of the present invention, while (B) representsthe case of the conventional image processor.

FIG. 8 is a block diagram showing another embodiment of the presentinvention.

FIG. 9 is an explanatory drawing showing the functions of the selectorgroups 22 through 32 and the decoder 36a given in FIG. 8.

FIG. 10 is an explanatory drawing showing the sequences of processingsto be executed respectively when “vertical reduction and horizontalreduction”, “vertical reduction and horizontal enlargement”, “verticalenlargement and horizontal reduction” and “vertical enlargement andhorizontal enlargement” are selected.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in detail in the following,referring to accompanying drawings.

FIG. 1 shows an embodiment of the present invention, wherein 10represents a terminal for inputting digital video signal (hereinafterreferred to simply as video signal) and 12, a terminal for outputtingthe video signal which has undergone image processing.

14 represents a contour correction circuit for contour correctionprocessing; 16, a horizontal characteristic variable filter forexecuting the filter processing for corresponding one of the horizontalimage enlargement and horizontal image reduction on the basis of the2-bit enlargement/reduction selection signal, which will be describedlater; 18, a vertical characteristic variable filter for executing thefilter processing for corresponding one of the vertical imageenlargement and vertical image reduction on the basis of theenlargement/reduction selection signal; 20, a frame memory as an exampleof the image memory.

22, 24, 26 and 28 represent a first, a second, a third and a fourthselectors for selecting one of the four inputs, A, B, C and D, forY-output according to the selection signal, which will be describedlater.

30 and 32 represent a fifth and a sixth selectors for selecting one of 2outputs, A and B, for Y-output according to selection signal, which willbe described later.

34 represents a terminal for inputting 2-bit enlargement/reductionselection signal for selecting one of the image enlargement processingand image reduction processing in horizontal direction and verticaldirection respectively; the image enlargement/reduction selection signalis input, as a selection signal like one shown in FIG. 4, to the first,second, third and fourth selectors, 22, 24, 26 and 28.

In other words, the first, second, third and fourth selectors, 22, 24,26 and 38, selectively outputs one of the outputs, A, B, C and D,according to the enlargement/reduction selection signals, “00”, “01”,“10” and “11”.

36 represents a decoder for decoding the enlargement/reduction selectionsignal to output the decoded signal as selection signal to the fifth andsixth selectors 30 and 32 as shown in FIG. 4. In other words, thedecoder 36 outputs L-level signal based on the enlargement/reductionselection signals “00”, “01” and “10” and outputs H-level signal basedon the enlargement/reduction signal “11”. Further, the fifth and sixthselectors, 30 and 32, respectively selects, for output, A input and Binput based on L-level and H-level signals.

38 represents an EPROM (Erasable Programmable Read Only Memory), and theEPROM 38 previously stores the coefficient data for image enlargementand image reduction, each with respect to horizontal direction andvertical direction.

40 represents a horizontal RAM (Random Access Memory) for the write-inand read-out of the coefficient data for both the image enlargement andimage reduction in horizontal direction; 42, a vertical RAM for write-inand read-out of the coefficient data for image enlargement and imagereduction in vertical direction; 44, a control circuit.

The control circuit 44 operates according to the enlargement/reductionselection signal inputted to the input terminal 34 and performs thefollowing functions {circle around (1)} and {circle around (2)}according to a control program which is not shown in the drawings.

{circle around (1)} Outputting address signal and R/W (Read/Write)signal, corresponding to PROM 38, horizontal RAM 40 and vertical RAM 42,according to the enlargement/reduction selection signals, “00”, “01”,“10” and “11” and reading from the EPROM 38 the coefficient data for“vertical reduction and horizontal reduction”, “vertical reduction andhorizontal enlargement”, “vertical enlargement and horizontal reduction”and “vertical enlargement and horizontal enlargement” for output to thehorizontal characteristic variable filter 16 and vertical characteristicvariable filter 18 by way of the horizontal RAM 40 and vertical RAM 42.

{circle around (2)} Outputting an enable signal to horizontalcharacteristic variable filter 16, vertical characteristic variablefilter 18 and frame memory 20 according to the enlargement/reductionselection signal “00” (i.e., vertical reduction and horizontalreduction).

Further, outputting an enabling signal to the vertical characteristicvariable filter 18 according to the enlargement/reduction selectionsignal “01” (vertical reduction and horizontal enlargement”) and alsooutputting a read-enable signal to horizontal characteristic variablefilter 16 and frame memory 20.

Further, outputting the enabling signal to the horizontal characteristicvariable filter 16 and outputting a read-enabling signal to the verticalcharacteristic variable filter 18 and to the frame memory 20 accordingto the enlargement/reduction signal “10” (vertical enlargement andhorizontal reduction).

Further, outputting the read-enabling signal to the horizontalcharacteristic variable filter 16, vertical characteristic variablefilter 18 and frame memory 20 according to enlargement/reductionselection signal “11” (vertical enlargement and horizontal enlargement).

As shown in FIG. 2, the contour correction circuit 14 comprises avertical contour sampler 51 for sampling the contour component invertical direction from the video signal inputted to an input terminal50, a horizontal contour component sampler 52 for sampling the contourcomponent in horizontal direction from the inputted video signal, afirst adder 53 for adding the contour component in vertical direction tothe contour component in horizontal direction and a second adder 55 foradding the contour component outputted from the first adder to theinputted video signal for output to an output terminal 54.

The vertical contour sampler 51 comprises delayers 56, 57, 58 and 59 forsequentially delaying, for 1 line (1H), the video signal inputted to theinput terminal 50, a multiplier 61 for multiplying the video signalinputted to the input terminal 50 by coefficient Kv1 for output,multipliers 62, 63, 64 and 65 for multiplying the output signals fromthe delayers 56, 57, 58 and 59 by coefficients Kv2, Kv3, Kv4 and Kv5respectively for output and an adder 66 for adding the output signalsfrom the multipliers 61 through 65.

The coefficients, Kv1, Kv2, Kv3, Kv4 and Kv5, are set, for example, to0, −¼, ½, −¼ and 0 when the input video signal is one for interlacescanning, while the same are set to −¼, 0, ½, 0 and −¼ when the inputvideo signal is one for non-interlace scanning.

The horizontal contour sampler 52 comprises delayers 67, 68, 69 and 70for sequentially delaying for 1 dot (1D) the video signals outputtedfrom the delayer 57 of the vertical contour sampler 51, a multiplier 71for multiplying, for output, the video signal outputted from the delayer57 by coefficient Kh1, multipliers 72, 73, 74 and 75 for multiplying theoutput signals from the delayers 67, 68, 69 and 70 by coefficients Kh2,Kh3, Kh4 and Kh5 respectively for output and an adder 76 for adding theoutput signals from the multipliers 71 through 75.

The coefficients Kh1, Kh2, Kh3, Kh4 and Kh5 are set, for example, to 0,−¼, ½, −¼ and 0 respectively when the input video signal is forinterlace scanning, while the same are to −¼, 0, ½, 0, −¼ when the inputsignal is for non-interlace scanning.

Delayers 77 and 78 for sequentially delaying input signal for 1 dot(1D), a noise coring circuit 79, a non-linear contour correction circuit80 and a vertical contour correction circuit 81 are interposed betweenthe output side of the vertical contour sampler 51 and one of the inputsides of the first adder 53.

A noise coring circuit 82, a non-linear processing circuit 83 and ahorizontal contour correction circuit 84 are interposed between theoutput side of the horizontal contour sampler 52 and the other inputside of the first adder 53.

As shown in FIG. 3, the horizontal characteristic variable filter 16comprises delayers 86 ₁, 86 ₂, 86 ₃, . . . . 86 _(n) with EN terminalsfor sequentially delaying for 1 dot the video signals inputted to theinput terminal 85 for output, a multipliers 87 ₀, 87 ₁, 87 ₂, 87 ₃, . .. 87 _(n) for multiplying the video signal inputted to the inputterminal 85 by coefficient data respectively for output and an adder 89for adding the output signals from the multipliers 87 ₀, 87 ₁, 87 ₂, 87₃ . . . 87 _(n) for output to an output terminal 88.

The delayers 86 ₁, 86 ₂, 86 ₃ . . . 86 _(n) are, for example, D-typeflip-flop's, each with EN terminal, and the enabling signal(read-enabling signal for enlargement and enabling signal for reduction)is input to the EN terminal from the control circuit 44. The coefficientdata for horizontal enlargement and horizontal reduction read out fromthe EPROM 38 and horizontal RAM 40 by the function {circle around (2)}of the control circuit 44 are input to the multipliers 87 ₀, 87 ₁, 87 ₂,87 ₃, . . . 87 _(n).

The vertical characteristic variable filter 18 has a composition similarto that of the horizontal characteristic variable filter 16 except thatthe delayers 86 ₁, 86 ₂, 86 ₃, . . . 86 _(n) are respectively replacedwith those capable of sequentially delaying the video signals for 1 linefor output. More particularly, the enabling signal (read-enable signalfor enlargement and enabling signal for reduction) is input to each ENterminal of each delayer for the 1-line delay, while the coefficientdata for vertical enlargement and vertical reduction, read out from theEPROM 38 and RAM 42 by the function {circle around (2)} of the controlcircuit 44, are inputted to the multipliers respectively connected tothe output sides of the delayers for 1-line delay.

Next, the operation of the embodiment shown in FIG. 1 will be describedreferring to FIGS. 2 through 7.

First, in the following section (1), it will be explained that eitherthe horizontal characteristic variable filter 16 or verticalcharacteristic variable filter 18 performs corresponding filterprocessing for image enlargement or image reduction according to the2-bit enlargement/reduction selection signal inputted to input terminal34; in section (2), the operations of the selector groups 22, 24, 26,28, 30 and 32 according to the enlargement/reduction selection signalwill be explained; in section (3), the sequence of processing for eachof “vertical reduction and horizontal reduction”, “vertical reductionand horizontal enlargement”, “vertical enlargement and horizontalreduction” and “vertical enlargement and horizontal enlargement” will beexplained; in section (4), the specific operation of the contourcorrection circuit will be explained.

(1) Operation of Characteristic Variable Filters 16 and 18

(i) Responding to the enlargement/reduction selection signals, “00”,“01”, “10” and “11”, the coefficient data for “vertical reduction andhorizontal reduction”, “vertical reduction and horizontal enlargement”,“vertical enlargement and horizontal reduction” and “verticalenlargement and horizontal enlargement” are read out from the EPROM 38by the function (1) of the control circuit 44 and are inputted to thehorizontal characteristic variable filter 16 and the verticalcharacteristic variable filter 18 by way of the horizontal RAM 40 andvertical RAM 42.

More particularly, as shown in FIG. 3, for the operation of thehorizontal characteristic variable filter 16, the coefficient data forhorizontal enlargement or horizontal reduction read out from the EPROM38 and the horizontal RAM 40 is inputted to the multipliers 87 ₀, 87 ₁,87 ₂, 87 ₃, . . . 87 _(n) respectively. The same applies to the verticalcharacteristic variable filter 18.

(ii) The enable signals corresponding to the horizontal characteristicvariable filter 16 and the vertical characteristic variable filter 18are inputted by the function {circle around (2)} of the control circuit44 responding to the enlargement/reduction selection signals “00”, “01”,“10” and “11”.

More particularly, as shown in FIG. 3, for the operation of thehorizontal characteristic variable filter 16, the read enabling signalis inputted to the EN terminal of each of the delayers 86 ₁, 86 ₂, 86 ₃,. . . 86 _(n) when the horizontal enlargement processing is selected,while the enabling signal is inputted when the horizontal reductionprocessing is selected. The same applies to the vertical characteristicvariable filter 18.

(iii) Therefore, when the enlargement/reduction selection signal is “01”or “11” (i.e., when the first bit is 1), the horizontal characteristicvariable filter 16 executes the filter processing for horizontalenlargement according to the coefficient data for horizontal enlargementand the inputted read-enabling signal, while the horizontalcharacteristic variable filter 16 executes the filter processing forhorizontal reduction according to the coefficient data for horizontalreduction and inputted enabling signal when the enlargement/reductionselection signal is “00” or “10” (i.e., when the second bit is 0).

Similarly, when the enlargement/reduction selection signal is “10” or“11” (i.e., when the second bit is 1), the vertical characteristicvariable filter 18 executes the filter processing for verticalenlargement according to the coefficient data for vertical enlargementand the inputted read-enabling signal, while the vertical characteristicvariable filter 18 executes the filter processing for vertical reductionaccording to the coefficient data for vertical reduction and theinputted enabling signal.

(2) Operations of Selector Groups 22 through 32

The first, second, third and fourth selectors, 22, 24, 26 and 28, selectthe inputs, A, B, C and D, respectively according to theenlargement/reduction selection signals, “00”, “01”, “10”and “11”.

Decoder 36 outputs the L-level signal according to theenlargement/reduction selection signals, “00”, “01” and “10”, whileoutputting H-level signal according to the enlargement/reductionselection signal “11”, so that the fifth and sixth selectors, 30 and 32,select A-input according to the enlargement/reduction selection signal,“00”, “01” and “10”, while selecting B-input according to theenlargement/reduction selection signal “11”.

(3) Order of Various Processings

When “vertical reduction and horizontal reduction”, “vertical reductionand horizontal enlargement”, “vertical enlargement and horizontalreduction” or “vertical enlargement and horizontal enlargement” isselected by the operations described in sections (1) and (2), theprocessing of the video signal inputted to the input terminal 10 by thecontour correction circuit 14, horizontal characteristic variable filter16, vertical characteristic variable filter 18 and frame memory 20 isexecuted in the order described in the following sub-sections (a), (b),(c) and (d), the details of which is given below respectively.

(a) When Vertical Reduction and Horizontal Reduction are Selected:

(i) When the enlargement/reduction selection signal is “00”, the videosignal inputted to the input terminal 10 is inputted, for processing, tothe horizontal characteristic variable filter 16 by way of the A-inputand Y-output of the first selector 22, and this is followed by theinput, for processing, to the vertical characteristic variable filter 18by way of the A-input and Y-output of the second selector 24, the input,for re-sampling, to the frame memory 20 by way of the A-input andY-output of the third selector 26, the input, for processing, to thecontour correction circuit 14 by way of the A-input and Y-output of thefourth selector 28 and the A-input and Y-output of the fifth selector 30and the output to the output terminal 12 by way of the A-input andY-output of the sixth selector 32.

(ii) As explained in the section (1), when enlargement/reductionselection signal is “00”, not only the horizontal characteristicvariable filter functions as the horizontal reduction filter but alsothe vertical characteristic variable filter functions as the verticalreduction filter.

Therefore, as shown in FIG. 5(a), the video signal inputted to the inputterminal 10 undergoes the horizontal reduction processing by thehorizontal characteristic variable filter 16 and the vertical reductionprocessing by the vertical characteristic variable filter 18, and thisis followed by the sampling by the frame memory 20 and the contourcorrection by the contour correction circuit 14.

Thus, as shown in FIG. 6(A), the image reduction processing is followedby re-sampling and contour correction, meaning that the band ofhigh-pass frequency component will not be restricted emphasized by thecontour correction in the stage of the image reduction processing unlikethe conventional case where the contour correction is made after theimage reduction processing (Refer to the case of FIG. 6(B)).

In other words, when the frequency characteristic of the original signal(inputted video signal) sampled at frequency Fs is as shown in FIG.6(A)(a), the band of frequency is limited by reduction filter as shownin FIG. 6(A)(b), and this is followed by the re-sampling processing(thinning processing) at frequency Fs/2 as shown in FIG. 6(A)(c) andcontour correction as shown in FIG. 6(A)(d).

With this contour correction, the high-pass component is emphasized toproduce contour correction effect as represented by the hatched areas inFIG. 6(A)(d).

In contrast, as shown in FIG. 6(B), in the case for comparison where theimage reduction processing is executed after the contour correction, thehigh-pass frequency component is emphasized as represented by thehatched area in FIG. 6(B)(b); the high-pass frequency component islimited with respect to frequency band by reduction filter as shown inFIG. 6(B)(c) and is then re-sampled (thinning processing) at frequencyFs/2, and, as a result, the contour correction becomes ineffective asshown in FIG. 6(B)(d).

(b) When Vertical Reduction and Horizontal Enlargement is Selected:

(i) When the enlargement/reduction selection signal is “01”, the videosignal inputted to the input terminal 10 is input, for processing, tothe vertical characteristic variable filter 18 by way of the B-input andY-output of the second selector 24, and this is followed by the input,for re-sampling, to the frame memory 20 by way of B-input and Y-outputof the third selector 26, the input, for processing, to the horizontalcharacteristic filter 16 by way of B-input and Y-output of the firstselector 22, input, for processing to the contour correction circuit 14by way of B-input and Y-output of the fourth selector 28 and A-input andY-output of the fifth selector 30, and the output to the output terminal12 by way of A-input and Y-output of the sixth selector 32.

(ii) As discussed in the previous section (1), when theenlargement/reduction selection signal is “01”, not only the horizontalcharacteristic variable filter 16 functions as a horizontal enlargementfilter but also the vertical characteristic variable filter 18 functionsas a vertical reduction filter.

Therefore, as shown in FIG. 5(b), the video signal inputted to the inputterminal 10 undergoes the vertical reduction processing by verticalcharacteristic variable filter 18, re-sampling by the frame memory 20,horizontal enlargement processing by the horizontal characteristicvariable filter 16 and the contour correction processing by the contourcorrection circuit 14.

Thus, the contour correction effect, similar to that in the case givenin (a), can be obtained without fear of getting the contour correctioneffect lost like in the case of the conventional system.

(c) When Vertical Enlargement and Horizontal Reduction are Selected:

(i) When the enlargement/reduction selection signal is “10”, the videosignal inputted to the input terminal 10 is inputted, for processing, tothe horizontal characteristic variable filter 16 by way of C-input andY-output of the first selector 22, followed by the input, forre-sampling, to the frame memory 20 by way of the C-input and Y-outputof the third selector 26, the input, for processing, to the verticalcharacteristic variable filter 18 by way of C-input and Y-output of thesecond selector 24, the input, for processing, to the contour correctioncircuit 14 by way of C-input and Y-output of the fourth selector 28 andA-input and Y-output of the fifth selector 30, and the output to theoutput terminal 12 by way of A-input and Y-output of the sixth selector32.

(ii) When the enlargement/reduction selection signal is “10”, asdescribed in (1), not only the vertical characteristic variable filter18 functions as a vertical enlargement filter but also the horizontalcharacteristic variable filter 16 functions as a horizontal reductionfilter.

Therefore, as shown in FIG. 5(c), the video signal inputted to the inputterminal 10 undergoes the horizontal reduction filter processing by thehorizontal characteristic variable filter 16, re-sampling by the framememory 20 and vertical enlargement filter processing by the verticalcharacteristic variable filter 18 and the contour correction by thecontour correction circuit 14.

Thus, the contour correction effect similar to that in the case of (a)can be obtained, without causing the contour correction effect to belost like in the case of the conventional system.

(d) When Vertical Enlargement and Horizontal Enlargement are Selected:

(i) When the enlargement/reduction selection signal is “11”, the videosignal inputted to the input terminal 10 is input, for processing, tothe contour correction circuit 14 by way of B-input and Y-output of thefifth selector 30, followed by the input, for re-sampling, to the framememory 20 by way of D-input and Y-output of the third selector 26, theinput, for processing, to the horizontal characteristic variable filter16 by way of D-input and Y-output of the first selector 22, the input,for processing, to the vertical characteristic variable filter 18 by wayof D-input and Y-output of the second selector 24, and the output to theoutput terminal 12 by way of D-input and Y-output of the fourth selector28.

(ii) When the enlargement/reduction selection signal is “11”, asdescribed in (1), the vertical characteristic variable filter 18functions as a vertical enlargement filter, while the horizontalcharacteristic variable filter 16 functions as a horizontal enlargementfilter.

Therefore, as indicated in FIG. 5(d), the video signal, inputted to theinput terminal 10, undergoes the contour correction by the contourcorrection circuit 14, followed by the re-sampling by the frame memory20, horizontal enlargement filter processing by the horizontalcharacteristic variable filter 16, and vertical enlargement filterprocessing by the vertical characteristic variable filter 18.

Thus, as shown in FIG. 7 (A), appropriate contour correction can beobtained following (initial) contour correction, the re-sampling andsubsequent image enlargement processing.

In contrast, in the case of the conventional system, wherein the contourcorrection is made after the image enlargement processing, it resultsthat the portion not requiring any emphasis is emphasized as shown inFIG. 7(B).

More particularly, when the frequency characteristic of the originalsignal (input video signal) sampled at frequency Fs is similar to thatshown in FIG. 6(A)(a), the frequency characteristic of the signal, whichhas undergone contour correction by the contour correction circuit 14,becomes as shown in FIG. 7(A)(a), that is, the image enlargementprocessing is executed as shown in FIG. 7(A)(b) after the interpolationprocessing by the frame memory 20 at the frequency Fs. Therefore, asshown in FIG. 7(B), the portion of contour not requiring emphasis can beprevented from being emphasized.

In contrast, in the case of the example for comparison, the contourcorrection is made following the interpolation processing by the framememory 20 at frequency Fs and the image enlarging processing asindicated in FIG. 7(B)(a), causing unnecessary emphasizing of thecontour portion not requiring emphasizing.

(4) Operation of Contour Correction Circuit 14

(i) Vertical contour sampler 51 samples the contour component invertical direction from the video signal inputted to input terminal 50by the operation of delayers 56, 57, 58 and 59, multipliers 61, 62, 63,64 and 65 and adder 66.

Horizontal contour sampler 52 samples the contour component inhorizontal direction from the video signal inputted to the inputterminal 50 by the operation of the delayers 67, 68, 69 and 70, themultipliers 71, 72, 73, 74 and 75 and the adder 76.

(ii) The contour component sampled by the vertical contour sampler 51 isdelayed sequentially by 1 dot through the delayers 77 and 78, followedby the removal of noise component by having the components, whose levelsare lower than set level (e.g., 7), removed by noise (coring) circuit79, the non-linear processing by non-linear processing circuit 80, thecorrection of vertical contour emphasis by vertical contour correctioncircuit 81 and the subsequent input to one input side of the first adder53.

The non-linear processing by non-linear processing circuit 80 means theprocessing designed for applying the limiter to prevent unnatural imagefrom being produced by sampling the vertical contour component of (high)level, further, for example, meaning the processing wherein the absolutevalue of the amplitude of the contour component is suppressed within therange where the absolute value is higher than the set value S (e.g.suppression to a fixed value), while being emphasized within the rangewhere the absolute value is lower than the set value S (e.g.,emphasizing according to the linear characteristic of a coefficientlarger than 1).

(iii) For the contour component sampled by the horizontal contoursampler 52, the component lower than the set level (e.g. ,7) issuppressed by the noise (coring) circuit 82 to have its noise componentremoved, followed by the non-linear processing by the non-linearprocessing circuit 83, the correction of horizontal contour emphasis bythe non-linear processing circuit 83 and the input to the other inputside of the first adder 53. The non-linear processing by the non-linearprocessing circuit 83 is substantially similar to the nonlinearprocessing by the non-linear processing circuit 80.

(iv) The composite contour component obtained by the first adder 53 isadded to the video signal by the second adder 55 and is outputted fromoutput terminal 54. The video signal, corrected for contour and to beoutputted from the output terminal 54, becomes D-input of the thirdselector 26 and A-input of the sixth selector 32.

The description of the above embodiment is concerned with the casewhere, in order to enable the contour correction in both horizontal andvertical directions, the contour correction circuit is composed of thehorizontal contour sampler, vertical contour sampler, the first adderand the second adder, but the present invention is not limited to suchan embodiment and is also applicable to the image processor, wherein thecontour correction circuit comprises either the horizontal contoursampler or vertical contour sampler and the adder in order to executethe contour correction in either one of horizontal direction or verticaldirection.

The above embodiment is designed so that, when one of the horizontaldirection and vertical direction is related to image enlargementprocessing while the other is related to image reduction processing, inorder to prevent the contour correction effect from becoming ineffectiveas the result of the image reduction processing by the selector groups,the processing is set to proceed sequentially through the stages ofvertical characteristic variable filter, image memory, horizontalcharacteristic variable filter and contour correction circuit; when theenlargement/reduction selection signal is for vertical enlargement andhorizontal reduction, the processing is set to proceed sequentiallythrough the stages of the horizontal characteristic variable filter,image memory, vertical characteristic variable filter and contourcorrection circuit, but the present invention is not limited to thisarrangement.

For instance, where (the image processor) is arranged so that, when theenlargement/reduction selection signal for vertical reduction andhorizontal enlargement is selected by the selector groups, theprocessing is set to proceed sequentially through the stages of thecontour correction circuit, vertical characteristic variable filter,image memory and horizontal characteristic variable filter, while, whenthe enlargement/reduction selection signal for vertical enlargement andhorizontal reduction is selected, the processing is set to proceedsequentially through the stages of the contour correction circuit,horizontal characteristic variable filter, image memory and verticalcharacteristic variable filter, the system can be arranged so that, whenone of the horizontal direction and vertical direction is related toimage enlargement processing while the other is related to imagereduction processing, the portion of the contour not requiring emphasisis prevented from being emphasized.

More particularly, when “vertical reduction and horizontal reduction”,“vertical reduction and horizontal enlargement”, “vertical enlargementand horizontal reduction” and “vertical enlargement and horizontalenlargement” are selected according to the enlargement/reductionselection signals “00”, “10” and “11”, the sequence of processing of thevideo signal inputted to the input terminal 10 in the stages of thecontour correction circuit 14, horizontal characteristic variable filter16, vertical characteristic variable filter 18 and frame memory 20 canbe set as given in FIG. 10(a), (b), (c) and (d), by altering C-input ofthe first selector 22 and B-input of the second selector as shown inFIG. 8 and by altering the function of the decoder 36 a as given in FIG.9.

With the arrangement described above, when the vertical reduction andhorizontal enlargement or vertical enlargement and horizontal reductionis selected, the horizontal enlargement processing or verticalenlargement processing is executed after the contour correction, wherebyit can be made possible that the portion (of the contour) not requiringemphasis is prevented from being emphasized in the image enlargementprocessing.

For the above embodiment, explanation is made as to the case where thecharacteristic variable filter comprises the horizontal characteristicvariable filter and vertical characteristic variable filter so that boththe image enlargement processing and image reduction processing can berelated to either one of the horizontal direction and vertical directionrespectively, but the present invention is not limited to this case,since the present invention is also applicable to the case where thecharacteristic variable filter comprises either one of the horizontalcharacteristic variable filter and vertical characteristic variablefilter. In this case, not only the composition of the selector group butalso the control of the coefficient read-out controller can besimplified.

INDUSTRIAL APPLICABILITY

As described in the foregoing, the present invention provides an imageprocessor capable of executing either one or both of the imageenlargement processing and image reduction processing, as well as theexecution of the contour correction processing, and is also capable ofeffecting appropriate contour correction, regardless of whether theimage enlargement processing or image reduction processing is selected.

What is claimed is:
 1. An image processor, comprising: a coefficientmemory for storing coefficient data for image enlargement and imagereduction; a coefficient read-out controller for reading outcorresponding coefficient data from the coefficient memory according toan enlargement/reduction selection signal; a characteristic variablefilter for executing filter processing corresponding to either imageenlargement processing or image reduction processing according to thecoefficient data read out by the coefficient read-out controller; animage memory; a contour correction circuit; and selector groups providedin preceding stage and subsequent stage of each characteristic variablefilter and image memory respectively and connected to one another,wherein the selector groups set the processing of an inputted videosignal to proceed sequentially through the contour correction circuit,image memory and characteristic variable filter when theenlargement/reduction selection signal is for image enlargementprocessing and the processing of the inputted video signal is set toproceed sequentially through the characteristic variable filter, imagememory and contour correction circuit when the enlargement/reductionselection signal is for image reduction processing.
 2. The imageprocessor according to claim 1, wherein the coefficient memorypreviously stores the coefficient data for image enlargement and imagereduction, each related with a horizontal direction or a verticaldirection; the coefficient read-out controller reads out from thecoefficient memory the corresponding coefficient data according to theenlargement/reduction selection signal for selecting either imageenlargement or image reduction, each related with either the horizontaldirection or vertical direction; the characteristic variable filtercomprises a horizontal characteristic variable filter for executingeither filter processing for image enlargement or image reduction and avertical characteristic variable filter for vertical image enlargementor reduction.
 3. An image processor comprising: a coefficient memory forstoring coefficient data for image enlargement and image reduction, eachrelated with a horizontal direction or a vertical direction; acoefficient read-out controller for reading out correspondingcoefficient data from the coefficient memory according to anenlargement/reduction selection signal and selecting either imageenlargement or image reduction, each related with either the horizontaldirection or vertical direction; a characteristic variable filter forexecuting filter processing corresponding to either image enlargementprocessing or image reduction processing according to the coefficientdata read out by the coefficient read-out controller, the characteristicvariable filter comprising a horizontal characteristic variable filterfor executing either filter processing for horizontal image enlargementor image reduction and a vertical characteristic variable filter forvertical image enlargement or image reduction; an image memory; acontour correction circuit; and selector groups provided in a precedingstage and subsequent stage of each characteristic variable filter andimage memory respectively and connected to one another, wherein when theenlargement/reduction selection signal for vertical reduction andhorizontal reduction is selected by the selector groups, the processingis set to proceed sequentially through the horizontal characteristicvariable filter, the vertical characteristic variable filter, the imagememory and the contour correction circuit; when theenlargement/reduction signal is for vertical reduction and horizontalenlargement, the processing is set to proceed sequentially through thevertical characteristic variable filter, image memory, horizontalcharacteristic variable filter and the contour correction circuit; whenthe enlargement/reduction selection signal is for vertical enlargementand horizontal reduction, the processing is set to proceed sequentiallythrough the horizontal characteristic variable filter, the image memory,the vertical characteristic variable filter and the contour correctioncircuit; and when the enlargement/reduction selection signal is forvertical enlargement and horizontal enlargement, the processing is setto proceed sequentially through the contour correction circuit, theimage memory, the horizontal characteristic variable filter and thevertical characteristic variable filter.
 4. An image processorcomprising: a coefficient memory for storing coefficient data for imageenlargement and image reduction, each related with a horizontaldirection or a vertical direction; a coefficient read-out controller forreading out corresponding coefficient data from the coefficient memoryaccording to an enlargement/reduction selection signal and selectingeither image enlargement or image reduction, each related with eitherthe horizontal direction or vertical direction; a characteristicvariable filter for executing filter processing corresponding to eitherimage enlargement processing or image reduction processing according tothe coefficient data read out by the coefficient read-out controller,the characteristic variable filter comprising a horizontalcharacteristic variable filter for executing either filter processingfor horizontal image enlargement or image reduction and a verticalcharacteristic variable filter for vertical image enlargement or imagereduction; an image memory; a contour correction circuit; and selectorgroups provided in a preceding stage and subsequent stage of eachcharacteristic variable filter and image memory respectively andconnected to one another, wherein when the enlargement/reductionselection signal for vertical reduction and horizontal reduction isselected by the selector groups, the processing is set to proceedsequentially through the horizontal characteristic variable filter, thevertical characteristic variable filter, the image memory and thecontour correction circuit; when the enlargement/reduction selectionsignal is for vertical reduction and horizontal enlargement, theprocessing is set to proceed sequentially through the contour correctioncircuit, the vertical characteristic variable filter, the image memoryand the horizontal characteristic variable filter; when theenlargement/reduction selection signal is for vertical enlargement andhorizontal reduction, the processing is set to proceed sequentiallythrough the contour correction circuit, the horizontal characteristicvariable filter, the image memory and the vertical characteristicvariable filter; and when the enlargement reduction selection signal isfor vertical enlargement and horizontal enlargement, the processing isset to proceed sequentially through the contour correction circuit, theimage memory, the horizontal characteristic variable filter and thevertical characteristic variable filter.
 5. An image processorcomprising: a coefficient memory for storing coefficient data for imageenlargement and image reduction; a correction read-out controller forreading out corresponding coefficient data from the coefficient memoryaccording to an enlargement/reduction selection signal; a characteristicvariable filter for executing filter processing corresponding to eitherimage enlargement processing or image reduction processing according tothe coefficient data read out by the coefficient read-out controller; animage memory; a contour correction circuit comprising a horizontalcontour sampler for sampling a contour component in a horizontaldirection, a vertical contour sampler for sampling a contour componentin a vertical direction, a first adder for adding the contour componentsampled by the horizontal contour sampler to the contour componentsampled by the vertical contour sampler and a second adder for adding acontour component outputted from the first adder to image data to beinputted to the contour correction circuit for outputting image datacorrected for contour; and selector groups provided in a preceding stageand subsequent stage of each characteristic variable filter and imagememory respectively and connected to one another, wherein the selectorgroups set the processing of an inputted video signal to proceedsequentially through the contour correction circuit, image memory andcharacteristic variable filter when the enlargement/reduction selectionsignal is for image enlargement processing and the processing of theinputted video signal is set to proceed sequentially through thecharacteristic variable filter, image memory and contour correctioncircuit when the enlargement/reduction selection signal is for imagereduction processing.